Collagen protein, such as animal glue, is an adhesive of great versatility with broad acceptance in industry. This natural polymer is an organic colloid derived from collagen, a protein constituent of the skins, hoofs, bones and connective tissue of animals, principally cattle. Animal glue is actually obtained by boiling the skins, hoofs, bones and the like, of such animals to a jelly.
Collagen protein, such as animal glue, has been used as an adhesive since earliest times. The stability and durability of this product is attested by the fact that antique furniture made two or three hundred years ago using animal glue as the adhesive can still be found today with firm and strong glue bonds. Therefore, in use since earliest times and in good supply, the modern animal glue collagen protein is usually produced from the hides or bones of either cattle or pigs. In 1681 bone glues were being produced by steam heating a pressure vessel. Today's procedures are well ordered and primarily consist of a succession of extraction processes. The following is a stylized flow sheet. ##STR1##
As the technology of manufacturing animal glues is old, and each industry has developed its own methods and procedures, large technological advances are somewhat rare. The chemistry is dependent on the excess pendant groups and the polarity of the macromolecule. The pendant groups consist of amines, acids, and alcohols, and undergo the typical reactions of those compounds. The polarity of the macromolecule makes this product extremely resistant to all solvents except water. Proper crosslinkage (tannage) after placement improves the water resistance immeasurably.
Although the product is a true protein and completely non-toxic, it is an exceptionally poor source of foods.
The amino acid analysis of various animal glues has been well established. The analysis is very similar regardless of the starting source, varying only by a percent or so.
______________________________________ Type A Type B Type B (Porkskin) (Skin) (Bone) ______________________________________ Alanine 8.6-10.7 9.3-11.0 11.3 Arginine 8.3-9.1 8.55-8.8 9.0 Aspartic Acid 6.2-6.7 6.6-6.9 6.7 Cystine 0.1 Trace Trace Glutamic Acid 11.3-11.7 11.1-11.4 11.6 Glycine 26.4-30.5 26.9-27.5 27.2 Histidine 0.85-1.0 0.74-0.78 0.7 Hydroxylysine 1.04 0.91-1.2 0.76 Hydroxyproline 13.5 14.0-14.5 13.3 Isoleucine 1.36 1.7-1.8 1.54 Leucine 3.1-3.34 3.1-3.4 3.45 Lysine 4.1-5.2 4.5-4.6 4.36 Methionine 0.8-0.92 0.8-0.9 0.63 Phenylalanine 2.1-2.56 2.2-2.5 2.49 Proline 16.2-18.0 14.8-16.35 15.5 Serine 2.9-4.13 3.2-4.2 3.73 Threonine 2.2 2.2 2.36 Tyrosine 0.44-0.91 0.2-1.0 0.23 Valine 2.5-2.8 2.6-3.4 2.77 ______________________________________
The major variation in various types of animal glue is in the molecular weight of the various extractions. This molecular weight difference accounts for the wide variation in socalled bloom strength and viscosity of the solution. The following table gives the bloom strengths of the various grades of animal hide glue.
______________________________________ National Association Peter Cooper of Glue Bloom Grams Millipoise Standard Manufacturers Mid- Value Grade Grade Range Point (Minimum) ______________________________________ 5A Extra 18 495-529 512 191 4A Extra 17 461-494 477 175 3A Extra 16 428-460 444 157 2A Extra 15 395-427 411 145 A Extra 14 363-394 379 131 #1 Extra 13 331-362 347 121 #1 Extra Special 12 299-330 315 111 #1 11 267-298 283 101 1XM 10 237-266 251 92 1X 9 207-236 222 82 11/4 8 178-206 192 72 13/8 7 150-177 164 62 11/2 6 122-149 135 57 15/8 5 95-121 108 52 4 70-94 82 42 3 47-69 58 2 27-46 36 1 10-26 18 ______________________________________
The prior art thermal insulating materials for the most part have one or more major drawbacks. For example, polystyrene and polyurethane foams are usually highly flammable; whereas the flame retardant types have a tendency to produce significant quantities of toxic smoke when a fire occurs. The prior art cellulose insulation materials include either inorganic flame retardants which leach out over periods of time, or organic flame retardants which produce large quantities of toxic smoke. The prior art thermal insulating materials such as fiberglass and mineral wool are suspected carcinogens and, in addition, are often backed by paper which is readily combustible.
The animal glue collagen protein thermal insulating foam of the present invention, on the other hand, is naturally fire retardant, it is smokeless, and it has products of combustion which have an extremely low toxicity. The insulating foam of the invention has a relatively high thermal insulation factor of the order of R 3.91/inch. The foam, moreover, is not attractive as food to rats, mice, cockroaches, or the like. The dry density of the foam is of the order of 0.5 pcf.
The animal glue collagen protein foam of the invention may be produced by appropriate foaming apparatus, such as described in Copending Application Serial No. (K-2418). The foam may be marketed in dry sheets designed, for example, to press-fit into stud cavities with no additional support of any kind being required. Alternatively, the foam may be marketed as a dry granule composition, to be applied wet by appropriate foaming apparatus at the site.
The difficulty in producing animal glue collagen protein foam lies in assuring that the foam will dry without collapsing at the ambient temperature at which it is to be used. This difficulty is overcome, in accordance with the method of the present invention, by establishing the gel formation temperature of the foam at at least 10.degree. F. above the highest expected ambient temperature. For example, if the ambient temperature is to be at or below 75.degree. F., the gel temperature should be in a range of 85.degree.-95.degree. F.
An appropriate collagen protein for the formation of the foam of the invention, as described above, is clear animal glue. Clear animal glues of any bloom strength from any source may be utilized, as long as they are properly compounded. However, gel temperatures are dependent to some extent on the bloom strength of the glue, and if the resulting gel temperature for a particular bloom strength is below the temperature required to withstand maximum ambient temperature, another collagen protein ingredient such as gelatin must be added to bring the gel temperature to the desired level. The critical consideration is matching the gel temperature of the solution to the expected maximum ambient temperature to be encountered.